In refrigeration systems, a typical refrigeration unit includes at least one chamber which is cooled to low temperature. The chamber is accessed by a door which, when closed, creates a seal to preserve the low temperature in the chamber. However, because of this seal, the chamber may periodically trap high temperature and high moisture-level air when the door is open and closed. Once trapped inside the sealed chamber, this warm wet air is rapidly cooled and contracts to create a low pressure in the chamber space. The resulting pressure differential between the inside and outside of the refrigeration unit chamber can present undesirable structural stresses on the unit and prevent ready re-opening of the chamber door. This pressure differential can be markedly higher in various ultra low temperature storage chambers created by industrial strength refrigeration units, such as those using cascading coil arrangements. The extreme pressure differentials created in such ultra low temperature chambers can affect the structural integrity of the device and severely reduce the practical use of the refrigeration unit.
A number of devices to equalize this pressure differential have been developed, many of which are called “pressure equalization ports”, or, alternatively, pressure relief ports, vents, or ventilators. All of the devices provide for a flow lumen or passage to be disposed between the sealed chamber and the outside of the refrigeration unit, so as to allow the flow of air therebetween. This flow allows high pressure air outside the unit to flow into the chamber when a low pressure develops, thereby equalizing pressure between the inside and outside of the unit. Pressure equalization ports and other pressure equalization devices serve the purpose of reducing the time required to open a pressurized door and access a refrigeration chamber. This time differential can be over 5 minutes, depending on pressure and port size.
With regard to port size, the flow passage cannot be so large as to allow significant heat losses, thereby negating the refrigeration achieved by the unit. The ports are therefore generally small in relation to the size of the refrigeration chamber and refrigeration unit. One drawback of existing ports is that the cooling of warm moist air in the refrigeration chamber tends to create condensation and ice crystals within the chamber. The relatively small size of flow passages and openings in existing pressure equalization ports tend to allow for the formation of ice crystals around the port as warm moist air flows through them. These ice crystals can accumulate to such a degree as to block the flow through the port. A need exists therefore, for a port that efficiently allows for equalization of pressure by providing effective flow pathways.
To improve operation, pressure equalization ports may include devices or features that heat the device and the flow through the device. Not only does this prevent the formation of condensation, but it also creates more of a pressure gradient, and therefore higher flow rates, through the port. Yet, adding such heating devices can complicate the structure of the refrigeration unit and create added costs in manufacturing and supplying the device with energy. The prior art devices supply heat energy through electric power sources, which can be inefficient in delivering thermal energy to the port, expensive in terms of energy used, and dangerous to operate and maintain. The efficiency of any heating device is also important in that adding any device generating heat near a refrigeration chamber can naturally reduce the effectiveness of the chamber. Therefore the heating apparatus and method should more effectively supply heat to the pressure equalization port without negatively affecting the overall performance of the refrigeration unit.
Accordingly, it is desirable to provide a method and apparatus for equalization of pressure differentials in refrigeration units which provides for effective flow pathways into a refrigeration chamber and efficiently prevents such flow pathways from obstruction while equalizing pressure in the chamber.